Adjustable coil differential gauge



1941- B. H. SCHWARZE ADJUSTABLE COIL DIFFERENTIAL GAUGE Filed Oct. 5, 1959 ,m/a. w y m,

Patented Jan. 21, 1941 rarest orrics ADJUSTABLE COIL DIFFERENTIAL GAUGE Bruce H. Schwarze, Flint, Mich, assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Application October 5,

3 Claims.

This invention relates to galvanome ters having two fixed coils and the novelty of the invention resides in the mechanism enabling the adjustment of both coils and the provision of a temperatme compensator to .aid in maintaining a.

constant field.

On the drawing Figure 1 is a view of'the galvanometer with the dial broken away better to show the construction.

Figure 2 is an enlarged section on the line 2-2 of Figure 1.

Figure 3 is an expanded view showing one of the coils and the adjustment means together with the compensator.

Figure 4 is a detailed perspective view of the pole piece end.

Referring to the drawing, the numeral 2 indicates the case of the galvanometer. The dial is indicated at 4 and is mounted on ears 6 formed on a frame 8 to which the coils Ill and I2 are secured. The coils are mounted on the frame by means of the integral ears I l and It. The axes of the coils are substantially at right angles to each other and at the place of intersection of the axes the shaft l8 of the pointer 20 is mounted. The pointer is secured to the shaft and there are also mounted on the shaft the balance wheel 22 and the armature 24 either of soft iron or magnetic material. The shaft E8 is held in place between the base of the frame 8 and an car 28 formed on the frame.

The frame is mounted in the case 2 by means of a threaded stud 28 passing through the frame and case and having a nut secured to the free end and tightly holding the frame in the bottom of the case 2. The frame has an insulating strip 30 mounted thereon and a plate on the underside of the insulating strip is secured thereto by means of the integral cars 32. The coil I2 is connected to a finger 34 on the plate by means of the lead 35, and the coil I is connected to a finger 38 by means of the lead 4!]. The finger 38 is in electrical connection with the terminal the end of which is shown in dotted outline at $2.

The right hand coil L2 is secured to a soft iron angle bracket 4 3 while the left hand coil It is secured to a brass angle bracket 45. The core of the coil l2 projects through an opening in the end of bracket M and is held on the bracket by means of a nut it is screwed onto a threaded end of the core. The left hand coil is similarly secured to the bracket to by means of the nut 418.

Each bracket is provided with a groove 55 on 1939, Serial No. 297,981

(Cl. I'll-$5) its outer face, the groove being parallel to the axis of the coil. A threaded opening 52 is provided in the bottom of the groove and a short threaded bolt 54 passes through an elongated slot 56 in the ear M of the frame and into the threaded opening 52 and holds the bracket 46 on the ear Hi. The ear M has suitable knobs or buttons 58 pressed therefrom and these knobs fit into the groove 50 to prevent lateral shifting of the bracket 416.

At the tip of the bracket 46 a nickel iron all-0y compensator 60 is secured. This compensator has the rightangularly ben t end 64 and the part 62 which is substantially at 45 to the axis of the coil. The permeability of this compensator changes with the temperature and at low temperature has a high permeability and at high temperature has a low permeability. It is inserted in the magnetic path to compensate for changes in the strength of the magnetic field due to the change in the resistance of the coil wires caused by temperature changes.

The right hand bracket 44 is shaped the same as the left hand bracket 45 and the difference in the mounting of the right hand side consists in the interposition of the pole piece (it. This pole piece extends around the shaft I 8 and with the armature 24 serves to concentrate the flux. The shape of this pole piece between the bracket M and the ear I6 is best shown in Figure 4. The pole piece has the turned over end 68 which is bent around the end of the ear l6 as best indicated in Figure 1. Where the pole piece faces the bracket M it is provided with the pressed out parts Ill which fit in the groove to in the bracket. The pol-e piece has the elongated slot 12 which mates with an elongated slot in the car It, this slot being the same as the slot 56 in the ear M. A second ear M is formed from the pole piece and bent over the opposite end of the ear it as is shown in Figure 1.

To adjust either coil the screw 54 is loosened sufficiently to allow a manual adjustment of either coil in either direction and when the proper position of the coil has been reached the screw is tightened rigidly to hold the coil in position.

This gauge is an improvement over the gauge shown in the Patent 1,942,529 to Bacon in that a more accurate calibration of the gauge is possible. This greater degree of calibration is particularly noticeable at the half reading and this more accurate degree of calibration is possible because of the use of two adjustable coils.

In instruments of this type the uniformity of the scale depends on the distance between the 5s armature and the ends of the coils and to a lesser degree upon the position of the pole piece 66. In the old type of instrument, the right hand coil gap was fixed and required very close manufacturing tolerances to insure proper calibration of intermediate points such as the one-half scale reading, but with the instrument of the present invention, since both coils are adjustable, wider manufacturing tolerances may be used and better uniform scale characteristics obtained.

I claim:

1. In a difierential gauge having two coils, a pointer, and an armature, two brackets on which the coils are mounted, one bracket for each coil, a frame on which the brackets are adjustably mounted, said adjustable mounting comprising a groove in the bracket, a slot in the frame, and a screw passing through the slot and screw threaded into the frame, and a plurality of projections on the frame fitting into the groove in the bracket to position the bracket and prevent lateral movement thereof.

. 2. In a differential gauge having two coils, a pointer, and an armature, two brackets on which the coils are mounted, one bracket for each coil, a frame on which the brackets are adjustably mounted, said adjustable mounting comprising a groove in the bracket, a slot in the frame, a screw passing through the slot and screw threaded into the frame, a plurality of projections on the frame fitting into the groove in the bracket to position the bracket and prevent lateral movement thereof, and a pole piece secured between the frame and one bracket, the end of the pole piece extending adjacent the armature.

3. In a difierential gauge having two coils, a pointer, and an armature, two brackets on which the coils are mounted, one bracket for each coil, 2. frame on which the brackets are adjustably mounted, said adjustable mounting comprising a groove in the bracket, a slot in the frame, a screw passing through the slot and screw threaded into the frame, a plurality of projections on the frame fitting into the groove in the bracket to position the bracket and prevent lateral movement thereof, and a pole piece secured between the frame and one bracket, the end of the pole piece extending adjacent the armature, said pole piece having projections thereon, said projections fitting into the groove to position the pole piece and prevent lateral movement.

BRUCE H. SCHWARZE. 

